He recovered from losing the opening three games in just seven minutes to shock the reigning champion 3-6, 7-5, 6-3.
"He deserved the victory", Djokovic said.
The market suggests, and my model agrees, that it's going to take more than this to beat Djokovic tomorrow, and Novak is likely going to have a real off-day if Tsitsipas is to cause a shock result.
"I was a bit fortunate to win that first set but I played okay and I fought extremely hard". He next plays 10th-seeded Fabio Fognini of Italy in the quarter-finals.
The world No.7 remained persistent and patient in lengthy exchanges to find the match-winning opportunity in the third set.
Top-seeded Djokovic is on a 24-0 sets winning streak in Asia dating back to last year's Shanghai Masters.More news: Sony Patent Reveals PlayStation VR 2 Headset
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Djokovic, a 16-time major victor, misfired a backhand to concede a break and a 3-1 deficit before Tsitsipas extended the gap with an ace.
It was a double celebration for the young Greek, who has also confirmed his place in the prestigious season-ending ATP Finals.
Fognini beat seventh-seeded Karen Khachanov of Russian Federation 6-3, 7-5.
Some people on social media have mentioned Tsitsipas" "clutch' ability and if such a phenomenon exists, it was on display against the improving Polish man, given that Tsitsipas saved four of his five break points, and converted one of his two - plus won the final set tiebreak. "Surely, yeah, that's what I tried to show today on the match and it worked out".
Fourth-seeded Dominic Thiem of Austria beat No. 15 Nikoloz Basilashvili 6-3, 6-4 and next faces 11th-seeded Matteo Berrettini. "I thought he took really a lot of good decisions, and he was super fast on his feet today, which I think made it really hard for me to get my freebies and winners off the baseline".
But the victory helped lift the Swiss maestro to an incredible 381 career victories at a Masters 1000 event, equalling Nadal.